1. Technical Field
The present invention relates to a method and apparatus for adjusting a screen gradient in a video display device such as a cathode ray tube (CRT) assembly in a monitor manufacturing line, and more particularly to a method and apparatus for adjusting a screen gradient in a video display device with minimal work from a skilled human operator by automatically testing and correcting the gradients of a screen of the cathode ray tube (CRT) and a front case in a monitor manufacturing line before assembling the cathode ray tube (CRT) and the front case.
2. Related Art
Generally, a video display device such as a cathode ray tube (CRT) as manufactured, for example, in U.S. Pat. No. 4,790,785 for Means And Method For Manufacture For A High Resolution Color Cathode Ray Tube issued to Lee et al., U.S. Pat. No. 4,950,192 for Method Of Manufacturing Of Color Display Tube issued to Rietdijk et al., U.S. Pat. No. 4,925,421 for Method For Manufacturing A Color Cathode Ray Tube And A Color Cathode Ray Tube issued to van den Broek, U.S. Pat. No. 5,136,428 for Flat-Plate Optical Device Having Gradient Index Of Refraction For Correcting Spatial Distortions issued to Ray, and U.S. Pat. No. 5,240,748 for Method Of Manufacturing A Display Window For A Display Device issued to Van Esdonk et al., must be tested and adjusted to correct display deviations and distortions.
Traditionally, the test and adjustment of display deviations and distortions mainly rely upon physical labor. More recently, advanced testing techniques using electro-optical systems such as disclosed in U.S. Pat. No. 4,757,239 for CRT Display System With Automatic Alignment Employing Personality Memory issued to Starkey, IV, U.S. Pat. No. 5,442,391 for Method And A System For Testing A Cathode Ray Tube Or Like Products issued to Hung et al., and U.S. Pat. No. 5,638,461 for Stereoscopic Electro-Optical System For Automated Inspection And/Or Alignment Of Image Devices On A Production Assembly Line issued to Fridge, are used to conduct necessary tests and adjustments on a production assembly line.
Typically, when power and a test pattern for testing the gradient are supplied to the CRT, a gradient line is horizontally displayed to the screen of the CRT. At this time, an operator adjusts the screen gradient by controlling the position of a front case of the CRT in order for a line formed by an outer surface of the front case to be parallel to the gradient line formed by the gradient test pattern. Afterwards, the gradient of the CRT is adjusted by fixing the front case to the CRT with a screw. Once the CRT and the front case are assembled, however, the gradient can only be adjusted if the screw is removed. As a result, the production assembly line becomes inefficient and the quality of the video display device is lowered. In addition, since the number of skilled human operators and the unnecessary operations increase in the production assembly line for testing the gradient of the CRT, productivity is reduced. Other techniques of adjusting the gradient before assembling the CRT and the front case are available. However, the common AC power and the gradient test pattern are supplied to the CRT through manual operation by way of a separate printed circuit board (PCB) assembly to the gradient adjusting apparatus.